The Mechanisms of Photochemical Reactions of o-Sulfobenzoic Imides

Article abstract of DOI:10.1246/bcsj.70.2051

The photochemical processes of N-propyl-o-sulfobenzoic imide to the amides were investigated in ethanol and monocyclic aromatics, such as benzene, anisole, toluene, polymethylbenzenes, and benzonitrile. It was clarified that although both the S₁ and T₁ states took part in those photochemical reactions, the mechanisms were different in ethanol and those aromatics. The mechanism in ethanol is thought to involve hydrogen-atom abstraction from ethanol by a diradical formed after the extrusion of sulfur dioxide. The mechanism in aromatics involved an energy transfer from the singlet excited aromatic molecules to the sulfobenzoic imide and the addition of the resulting diradicals to the partner aromatics. Although the sulfobenzoic imide sensitized to a triplet state by acetophenone in benzene resulted as well in the formation of the arylated benzamide, this process was minor in comparison with the process via the S₁ state. This was attributed to the triplet multiplicity of the diradical. The reactions of the sulfobenzoic imide with p-xylene and mesitylene were less predominant than those with toluene and anisole, which was attributable to a steric effect of plural methyl groups on the ring. The fact that no formation of the arylated benzamides took place in the case of benzonitrile could be explained by a strong inductitive effect of a cyano group of benzonitrile.